Key Concepts:
Vocabulary: human immunodeficiency virus (HIV), acquired immuno- deficiency syndrome (AIDS)
HIV/AIDS
What Is HIV/AIDS?
Main Idea: HIV/AIDS weakens the body’s immune system.
Human immunodeficiency virus (HIV) is a virus that attacks the immune system. Once HIV enters the body, it finds and destroys the white blood cells that fight disease. The final stage of an HIV infection is acquired immunodeficiency syndrome (AIDS), a disease in which the immune system is weakened.
AIDS has become one ofthe deadliest diseases in human history. More than 25 million people around the world have died of this disease, including more than 500,000 Americans. Health care officials estimate that currently 40 million people worldwide have HIV/AIDS. The statistics are alarming:
As Figure 24.7 shows, HIV infection is a worldwide concern. Health care officials consider HIV/AIDS a pandemic, a global outbreak of infectious disease. Many experts and scientists consider HIV/AIDS to be the most serious public health problem facing the world. The seriousness of the HIV/AIDS pandemic is greatly increased because many of the young people who are infected do not know it.
Understanding HIV/AIDS
Main Idea: HIV/AIDS is transmitted in a variety of ways.
HIV is a fragile viruS’·and cannot live outside the human body. Exposure to air at room temperature kills the virus. HIV cannot be spread through airborne transmission, through casual contact such as shaking hands or hugging, or from insect bites. Although the virus has been found in sweat, tears, and saliva of infected persons, the amount is too small to be considered dangerous.
HIV is transmitted among humans only when one person’s infected blood, semen, or vaginal secretions comes in contact with another person’s broken skin or mucous membranes.
HIV is spread in three ways:
During sexual intercourse. HIV can enter the blood- stream through microscopic openings in tissues ofthe vagina, anus, mouth, or the opening in the penis. People with STDs are more vulnerable to HIV infection because STDs cause changes in the body’s membranes that increase the likelihood of HIV transmission.
By sharing needles. Anyone who uses needles contami- nated with HIV allows the virus to enter directly into his or her bloodstream. Needles used for body piercings and tattoos also can come in contact with contaminated blood. If those needles are not properly cleaned or steril- ized, other customers ·can become infected.
From mother to baby. A pregnant female infected with HIV can pass the virus to her unborn baby through the umbilical cord, during childbirth, or through breast- feeding. If an expectant mother knows she’s infected, she can take medication that might prevent her child from contracting HIV. During childbirth, the doctor and nurses will work to prevent the newborn from coming into contact with the mother’s blood, and the mother will be asked not to breastfeed her infant. The number of infected infants has declined in the United States now that pregnant females are routinely tested for HIV.
How HIV/AIDS Affects the Immune System
HIV attacks the body’s immune system by destroying lymphocytes. These are specialized white blood cells that perform many immune functions, such as fighting patho- gens. As you learned in Chapter 23, there are two types of lymphocytes: B cells and T cells. Helper T cells stimulate B cells to produce antibodies, which help destroy pathogens that enter the body. When HIV enters certain cells, including lymphocytes, it reproduces itself and eventually destroys the cell. Figure 24.8 shows how HIV attacks cells. As more cells are destroyed, the immune system becomes weaker and weaker. The body then becomes vulnerable to AIDS-opportunistic illnesses, infections the body could fight off if the immune system were healthy.
HIV infection usually goes through identifiable stages before progressing to AIDS:
Middle stage. This stage occurs in about 40 to 70 percent of infected patients. Patients experience fever, headache, sore throat, rash, diarrhea, and enlarged lymph nodes.
Symptomatic stage. Helper T cells fall to 200 to 400 per milliliter of blood. The patient experiences flu-like symp- toms, such as headache, fever, body aches, swollen glands, diminished appetite, weight loss, and skin rashes.
AIDS stage. Helper T cells drop to less than 200, or one or more AIDS-opportunistic illnesses are present.
When the virus has destroyed or impaired most of the immune system’s white blood cells, the patient is in the final stage of HIV and is said to have AIDS. People with AIDS have immune systems that are so weakened that they may die from illnesses from which they would ordinarily recover.
Giving or Receiving Blood: Is It Safe?
Some people fear that they might be infected with HIV when donating or receiving blood. In the United States, health care professionals ·always use sterile needles to draw blood. In addi- tion, all donated blood has been tested for HIV since 1985. According to the CDC, “The U.S. blood supply is among the safest in the world.”
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